PCI: hv: Remove unused field pci_bus in struct hv_pcibus_device

PCI: hv: Remove unused field pci_bus in struct hv_pcibus_device

Field pci_bus in struct hv_pcibus_device is unused since
commit 418cb6c8e051 ("PCI: hv: Generify PCI probing"). Remove it.

No functional change.

Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Reviewed-by: Srivatsa S. Bhat (Microsoft) <srivatsa@csail.mit.edu>
Signed-off-by: Wei Liu <wei.liu@kernel.org>